bakoline

Hi there, I bought this particular red dot + laser and from the first day this part (see in pic) has a wobble, I have no idea how to make it tight, I try to take out battery cover but there is no any screw or anything. I would be very happy if you can help http://www.ebay.com/itm/Tactical-Holographic-Reflex-4-Reticles-Red-Green-Dot-Sight-Scope-w-Red-Laser-New-/281418433046?pt=LH_DefaultDomain_0&hash=item4185d88216